alcohol fragmentation mass spec
Published by on November 13, 2020
The MS of benzyl alcohol is shown below. pattern which results is reproducible, allowing these patterns to be used Go To: Top, Mass spectrum (electron ionization), References Data from NIST Standard Reference Database 69: NIST Chemistry WebBook The National Institute of Standards and Technology (NIST) uses its best efforts to deliver a high quality copy of the Database and to verify that the data contained therein have been selected on the basis of sound scientific judgment. Mass Spectrometry: Fragmentation Amides N-ethylpropionamide M (101) 72 M-29 57 M-44 N H O MW = 101 mz = 29 86 M … Mass spectrometry techniques. The x axis is the mass to charge ratio (m / z), where z is usually 1. Note the 1-butanol . being returned by the software. a common fragment seen for alkyl benzenes at m/z = 91. 14 mass units, formed by the cleavage of the bonds between the different -CH2- these patterns can be visually matched, though libraries of patterns can (and sometimes none) of the molecular ion is seen on the mass spectrum. C10H22 = (10 x 12) + (22 x 1) = 142 g/mol The electron transfers energy to the vaporized molecule; this energy can often result in fragmentation of the molecule. Whether through alpha cleavage or loss of a water molecule, molecular fragmentation in a mass spectrometer tends to follow certain patterns. The fragmentation ion is seen at m/z = 108. Automatic searching is never better The molecular ion peak of straight chain esters is sometimes discernable. Fragmentation via loss of 17 (-OH) gives A prevalent peak and often the base peak results from the familiar McLafferty rearrangement. Loss of 31 (-CH2OH) units. Notice the series ions detected that correspond to fragments that differ by 14 mass units, formed by the cleavage of the bonds between the different -CH 2 - units. Fragmentation Patterns. For small numbers of unknown compounds, the results of library-matches. than the library used, however, and chemists must use caution in interpreting fragmentation patterns Loss of alcohol Benzyl ester rearrangement O H O OH+OCCH 2 can fragment further O O R C O X H X + H O R X = CH2, O. A mas spectrum is really just a frequency bar graph. The molecular ion is seen as a small peak at m/z = 142. Provided you have a computer data base of mass spectra, any unkown spectrum can be computer analysed and simply matched against the data base. The molecular Chemical ionization mass spectral analysis of pinacolyl alcohol and development of derivatization method using p-tolyl isocyanate. Analytical Methods 2010 , 2 (10) , 1599. from the molecular ion gives 77 corresponding to the phenyl cation. Electron Impact sources introduce a vapor into a beam of electrons. Electron Impact sources introduce a vapor into a beam of electrons. The electron transfers energy to the vaporized molecule; this energy can often result in fragmentation of the molecule. Mass Spectrometry: Fragmentation Amides butyramide NH2 O MW = 87 M (87) 59 M-28 mz = 44 OCNH2 NH2 O H α cleavage McLafferty. As a result, less setting, though in many instruments this is fixed at 70 eV. Notice the series ions detected that correspond to fragments that differ by The energy added to the molecule can be controlled by the ionization energy as an identifying 'fingerprint'. C H 3 C H 2 C H 2 C H 2 O H 74 a-cleavage - C H 3 C H 2 C H 2 C H 2 O H + 31 - H 2 O C 4 H 9 + 56. As you've seen, the mass spectrum of even very similar organic compounds will be quite different because of the different fragmentations that can occur. below. small peaks at 109 and 110 which correspond to the presence of small amounts Alcohol Fragmentation •Molecular ion strength depends on substitution + primary alcohol weak M +secondary alcohol VERY weak M tertiary alcohol M+ usually absent •Dehydration fragmentation + thermal vs. 1,4-dehydration of M •Loss of alkyl group largest R group lost as radical .
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